An ink-jet recording apparatus uses ink to record images on a sheet. The ink-jet recording apparatus includes a mounting portion configured to mount thereon a plurality of ink cartridges. The ink cartridge is removably mountable on the mounting portion. Color inks are supplied from the ink cartridges to a recording head, the recording head selectively discharges ink from nozzles to the sheet. In this way, a color image is recorded on the sheet. In this type of ink-jet recording apparatus, an optical sensor is installed to the mounting portion or the ink cartridge in order to detect the amount of ink stored in the ink cartridge (for example, see JP-A-2007-152559).
FIGS. 14A and 14B are perspective views illustrating an optical sensor 280 used for a related-art ink-jet recording apparatus. FIG. 14A is a perspective view illustrating the internal configuration of the optical sensor 280, and FIG. 14B is a perspective view illustrating a plurality of optical sensors 280 attached to a wall 285 of the mounting portion. As shown in FIG. 14A, the optical sensor 280 includes a light-emitting element 281 and a light-receiving element 282. The light-emitting element 281 and the light-receiving element 282 are provided in a substantially U-shaped resin housing 283. The housing 283 is formed in a U-shape by coupling a plurality of members. A gap is formed between the members due to an undefined factor, such as a manufacturing tolerance. Light emitted from the light-emitting element 281 can leak from such gap. Therefore, in the related-art inkjet recording apparatus, as shown in FIG. 14B, the optical sensors 280 are arranged in the same direction, and partition plates 286 are provided between the sensors 280. In this way, light leaking from the gap between adjacent optical sensors 280 is shielded by the partition plate 286, and the light leaking from the gap is reduced or prevented from being incident on the light-receiving element 282 of another optical sensor 280. Therefore, it is possible to prevent the detection error of the optical sensor 280 due to light leakage.
However, when the partition plates 286 (see FIGS. 14A, 14B) are provided on the mounting portion, for mounting the ink cartridge, at least a space corresponding to the thickness of the partition plates 286 is reduced from the entire space. Therefore, it is necessary to increase the width of the mounting portion by a value corresponding to the thickness of the partition plates. If the size of the mounting portion increases, the size of the ink-jet recording apparatus also increases. In order to reduce the size of the mounting portion, it is conceivable that the partition plates 286 (see FIGS. 14A, 14B) are removed to reduce the gap between the ink cartridges and the gap between the optical sensors 280. However, in this case, the problem of the detection error of adjacent optical sensors 280 due to light leaking from the gap of the housing 283 arises.